Paleozoic
Cambrian The first period of Paleozoic. It is known from the "Biological explosion" in the beginning of the period. "Biological explosion" happened around 545 mya. It's hard to believe, but before it , no terms "predator" and "prey" even existed. By unknown reason at this time appeared first animal armour, to protect them from vicious carnivores. Earth's first really big predator was Anomalocaris. It was a crustacean up to a metre long with a bad attitude. But his main weapon were his eyes. Anomalocaris and other crustaceans - trilobites - were the first "eyed" creatures. In fact, trilobites were the most succesfull animals ever (after brachiopods). They survived from Early Cambrian to the Late Permian, that's more than 300 million years! Ordovician Towards the Ordovician peeriod Anomalocaris is replaced by more advanced invertebrates, such as orthocones. Orthocones were shelled streamline predatory mollusks. Some of the orthocone sreacheed 6 metres(20 feet) long - they were among the biggest predators in Paleozoic seas. However, in Ordovician happened another breakthrough - without hich we could never appear. First large vertebrates showed up. Among them were primitive sharks(gnathostomes) and small bony fish. Small vertebrates appeared even in Cambrian, but in Ordovician they reached sizes at lest bigger than a human hand! Silurian In Silurian period streamline orthocones are quickly outcompeted by eurypterids - large crustaceans, they are also known as "sea scorpions". But euripterids couldn't grow as large as orthocones - their maximum size was only 3 metres(10 feet) - because their carapace could not grow along with their bodies. Also the first plants appear on the land. They are called rhyniophyta - Cooksonia, Rhynia, Zosterophyllum ''The evolution of primitive jawless fish continues in Silurian. Appear armoured species - the placoderms. But they will not rule the Earth until the next period - the Devonian... '' Devonian Now fish rule the Earth. Giant placoderms - the arthrodirans - appear. Among them are well-known Dinichtis and Dunkleosteus. They both reach unpresidented size for their time - up to 9 metres! During Devonian another breakthrough happened - tetrapodisation of the lobe finned fishes. This means that first time in the prehistory, vertebrates(amphibians) walk on land. First amphibian genera are Acanthostega, Ichtyostega, Ventastega and Hynerpeton. Carboniferous This period is sometimes called the greenest. And it is really true. The percentage of oxygen was much higher than today - this allowed insects and plants grow to giant proportions. Strange plants Tomiodendrons had high stems with no branches; early conifers Calamits were identicall to today's cypress. Insects also grew very large. For example, in Carboniferous lived the biggest crustecean ever - Arthropleura. It was a giant millipide, up to 3 m long. In the skies flew huge dragonfly - Meganeura. Spiders (Mesothelae) the size of a human head crawled on the forest floor. But Carboniferous is famous for the third breakthrough in Earth history - during this time period appeared first aminiotes - reptiles. More about reptiles... In fact, reptiles are divided into 4 main groups: diapsids, euriapsids, synapsids and anapsids. Each group( apart from Anapsida) have openings in their skulls - entorganal fenestrae(e.f.). They are situated directly in front of an eye socket. Anapsids have 0 e.f, synapsids - 1, euriapsids 1.5 and diapsids 2. The first group to appear were anapsids. Next synapsids showed up and took up role as top predators. In Triassic diapsids became dominant animals. Permian In Permian synapsids became dominant land animals. Pelycosaurs, sail- backed reptiles like Dimetrodon, ruled Early Permian, and more advanced and abundant therapsids - the Late.Pelycosaurs were both plant(Edaphosaurus) and meat(Dimetrodon) eaters. However they also had similiarieties in the animal world. Platyhistricks, a land amphibian, was also sail backed.In the Late Permian pelycosaurs give up to therapsids. Therapsids also had their own ecosystem. Dicynodonts were herbivores, and cynodonts with gorgonopsians preyed upon them. Cynodonts first appeared in Middle Permian(Procynosuchus), and in Late Triassic gave rise to mammals.During this time archosaurs evolved(Archosaurus and Proterosuchus). In the future their descendants will rise to power: dinosaurs, pterosaurs and marine reptiles.